Apparatus for starting and protecting of electrical motors

ABSTRACT

A combined relay and protector is shown particularly suitable for starting and protecting electrical equipment having a main winding and a start winding comprising two thermal elements mounted along side one another with a combination heater located in heat transfer relation with both elements. A preferred embodiment shows one of the thermal elements as a creep acting blade connectable to the start winding and the other thermal element as a snap acting disc connectable to deenergize the motor. A second embodiment includes a shunt heater connected across the creep acting blade.

United States Patent [1 1 Perry 1 Feb. 27, 1973 [54] APPARATUS FOR STARTING AND PROTECTING OF ELECTRICAL MOTORS [75] Inventor:

[73] Assignee: Texas Instruments Incorporated,

Dallas, Tex.

[22] Filed: May 19, 1971 [21] Appl. No.: 144,959

Frederick G. Perry, Norton, Mass.

[52] US. Cl. ..337/95, 337/102, 337/336 [51] Int. Cl. ..H0lh 61/06 [58] Field of Search....337/40, 95, 96,102,105, 335, 337/336 [56] References Cited UNITED STATES PATENTS 2,506,272 5/1950 Koci ..337/96 X 2,786,171 3/1957 Clark ..337/95 X 2,658,175 11/1953 Clark ..337/40X 3,188,429 6/1965 Ehrens et al ..337/95 X Primary Examiner-Bernard A. Gilheany Assistant Examiner-F. E. Bell Attorney-l-larold Levine, Edward J. Connors, Jr., John A. l-laug, James P. McAndrews and Gerald B. Epstein [57] ABSTRACT A combined relay and protector is shown particularly suitable for starting and protecting electrical equipment having a main winding and a start winding comprising two thermal elements mounted along side one another with a combination heater located in heat transfer relation with both elements. A preferred embodiment shows one of the thermal elements as a creep acting blade connectable to the start winding and the other thermal element as a snap acting disc connectable to deenergize the motor. A second embodiment includes a shunt heater connected across the creep acting blade.

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[l re/2202* Q) Frederick 6- Per/y APPARATUS FOR STARTING AND PROTECTING OF ELECTRICAL MOTORS The present invention relates to thermal. switches, and more particularly to a device particularly useful in starting and protecting motors having a main winding and a start winding.

Such motors are customarily started by using a motor starting relay, either electromagnetically or thermally operated. An electromagnetic relay comprises essentially a relay coil cooperable with a movablearmature and associated contact structure so thatupon energization both the startand main windings are connected to a source of power but as the motor comes up to its normal running speed the electromagnetic field around the coil causes the armature to move and the contacts to open to thereby open the start circuit. Additional means is normally required to provide protection from various types of overloads. While this system can be very effective, it is inherently complex, bulkyand expensive due to'its many parts. On small fractional horsepower motors in particular it is desirable to have a compact, inexpensive yet reliable device to provide both the starting and protective functions.

As mentioned above thermally. operated relays are known in the art, some including the motor protection function such as disclosed and claimed in U.S. Pat. Nos. 3,112,384 and 3,146,378, both assigned to the instant assignee. I-Iowever,.for many uses, these prior art relays are still relatively complex and expensive as well as being difficult to match with the characteristics of small motors in particular and further their structures are not conducive to mass production techniques.

It is therefore an object of the present invention to provide a device for the starting and protecting of electric motors having astart winding'and a main winding which avoids the disadvantages of the prior art mentioned above.

Another object is the provision of such a device which is simple, reliable, inexpensive, compact and one which has a minimum of components.

Another object is the provision of a device for the starting and protecting of motors having a start winding and a main winding and which is particularly suited for matching the characteristics of such motors, especially small motors.

Yet another object is the provision of a motor starting relay which also provides protection for both start and main windings.

Another object is the provision of a motor starting relay which provides protection from the continued energization of both the start and main windings.

Other objects will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of the application of which .will be indicated in the appended claims.

In the accompanying drawings, in which several of the various possible embodiments are illustrated:

FIG. 1 is a front elevation of a device made in accordance with the instant invention;

FIG. 2 is a top plan view of the FIG. 1 device;

FIG. 3 is a side elevation of the FIG. 1 device;

FIG. 4 is a top plan view of the FIG. 1 device with the cover removed;

FIGS. 5 and 6 are cross sectional views taken along the lines 5-5 and 6-6 respectively of FIG. 4;

FIG. 6a is a broken away cross sectional view taken on lines 6a-6a of FIG. 4;

FIG. 7 is a top plan view similar to FIG. 4 but with the thermal elements partly broken away;

FIG. 8 is a schematic wiring diagram showing the electrical connections of the FIGS. 1-7 device as used with a motor;

FIG. 9 is a top plan view, similar to FIG. 4, of a second embodiment of the invention; and

FIG. 10 is a cross sectional view taken on lines 10- 10 of FIG. 9.

Dimensionsof certain of the parts as shown in the drawings may have been modified for the purpose of clarity of illustration.

Similar reference characters indicate corresponding parts throughout the several views of the drawings.

Turning now to the drawings, and particularly FIGS. 4-8, the combined motor protector-relay is generally indicated by numeral 10 and includes a generally rectangular base member 12. formed of electrically insulative material such as a phenolic resin, defining a switch cavity 14 therein. Base 12 is formed with a lip portion 16 around the periphery thereof for mating reception of cover 18 (FIGS. 1-3). Also formed in base l2on two diagonally opposite comers are raised portions 20,22 respectively, which extend beyond any of the component parts located within cavity 14 so that the component parts will be protected from damage, especially during manufacture and assembly of the device. A plurality of platforms 24, 26, 28 are provided on bottom wall 30 for mounting several components in desired locations. Mounted on platform 24, as best seen in FIG. 5, is an element 32 formed of thermostatic material such as bimetal. Element 32 is cantilever mounted, as by welding slug 34, which extends through an aperture in the blade, to a leg 36 of a multileg terminal 38, which terminal extends through bottom wall 30 and platform 24. Element 32 has a free end portion extending from leg 36 the shape of which may vary depending upon the specific motor characteristics to be matched. As shown in FIG. 4 it is trapezoidal in shape. Mounted on the free distal end portion of element 32 is an electrical contact 40 attached by conventional means, as by welding. Element 32 is preferably formed as a creep type blade with contact 40 adapted to move into and out'of engagement with leg 42 of terminal'44 which terminal extends through bottom wall 30 and platform 26. Terminal 44 can be formed of an electrically conductive material such as cold roll steel but leg 42 is preferably provided with a layer of a highly electrically conductive material such as copper or silver. This layer could be plated or inlayed for example, as desired. The trapezoidal configuration of blade 32 results in the distal portion thereof having less mass and hence permits the blade and movable contact to move into the disengaged position more readily as well as to remain in that position for a longer period of time.

Terminal 38, as mentioned above, is formed with a plurality of legs extending from a body portion 46. A transversely extending groove in platform 24 receives body portion 46 and a downwardly extending leg extends through an aperture in bottom wall 30. Leg 36, located intermediate the ends of body 46, which mounts the thermal element 32, is bent to lie along platform 24 and extends from the body 46 in a direction away from the center of body 12 while leg 48 formed at an end of body 46 and also bent in a direction parallel to the surface of platform 24 extends in a direction toward the center of body 12. Leg 48 is used to provide electrical connection to end 50 of a combined heater element 52. This connection can be effected in any conventional manner, as by welding. Heater 52, formed of a relatively high electrically resistive material such as nichrome, is configured to extend from leg 48 to a position underneath thermal element 32 so that a portion 54 runs along the longitudinal axis of thermal element 32 for a portion of its length while the remainder of the heater extends over to a second thermal element 72 and overlies element 72 in close heat transfer relation therewith for at least a portion of its length. End 56 of heater 52 is attached, as by welding, to welding slug 58 which in turn is used to cantilever mount thermal element 72 to base 12. As seen in FIG. 6a, slug 58 forms the head of a mounting stud 60 which is formed with a plurality of axially extending splines 62. The splined portion of the stud is received in an interference type fit in eyelet 64. The thermal element 72 is formed with an aperture in one end thereof which fits about portion 66 of stud 60 and is welded to slug 58 as indicated in the drawing. Platform 28 provides an increased thickness wall portion for adequate strength for mounting of the thermal element 72.

Thermal element 72, generally rectangular in shape, is formed of thermostatic material, such as bimetal, as is element 32 but is made into a snap acting element or disc. That is, element 72 is formed with a nondevelopable or dishedportion which causes it to move with snap-like motion from one configuration (e.g., concave) to an opposite one (e.g., convex) and back upon predetermined changes in temperature. As shown in the drawings, it is preferred that the dished portion actually includethe entire element in order to minimize creep action of the element prior to snap action. An electrical contact 74 is conventionally mounted on the free distal end of the element 72 as by welding, and is adapted upon snapping of the element to move into and out of engagement with leg 76 of L-shaped tenninal 78 which may be similar to terminal 44, referred to above, in material and construction. Calibration of element 72 is effected upon assembly by insertion of the splined stud 60 into eyelet 64 until desired contact pressure and opening temperature are obtained between contact 74 and stationary contact or leg 76.

Operation of the device will be explained particularly with reference to FIG. 8. A main winding MW and start winding SW of a motor are shown with one side of each winding connected to line voltage L. The other side of the start winding is connected to terminal 44. The other side of the main winding is connected to terminal 38 while terminal 78 is connected to the other side of line voltage. It will be noted from dashed line 80, FIG. 8, that both thermal elements, 32 and 72 are in heat transfer relation with heater 52. Both thermal elements are normally closed at the at rest, nonenergized condition. Upon energization of the device from power source 78, L through a switch (not shown) current passes from line 78 through contacts 76, 74, disc 72, heater 52 and divides at terminal 38 between creep element 32, contacts 40, 42 through the start winding and through the main winding to line L, both windings being energized. As current passes through the thermal elements some Ir heating occurs along with heat being transferred from heater 52 until element 32 reaches predetermined temperature by which time the main winding has attained normal operating speed and at which point element 32 deflects to open contacts 40, 42 deenergizing the start winding. Heater 52 remains energized and maintains element 32 in the contacts open position as long as device 10 is energized. As mentioned above, disc 72 is also heated by Ir heating as well as by heater 52. This however just maintains disc 72 at a conditioned temperature so that upon an overload, the additional heat generated (either by increased heat from the motor windings which are in heat transfer relationship with device 10, or from increased current levels) the disc will snap separating contacts 74, 76 thereby deenergizing the motor as well as heater 52 which allows the thermal element upon cooling to return to a reset position. Disc 72 provides protection for both motor windings from excessive current levels as well as preventing the condition when both windings are continually energized which condition could occur, for instance, if contacts 40, 42 should weld. That is, the start winding is generally of a fine high-resistance wire and generally can withstand continuous operation for only a short time. Should contacts 40, 42 weld the heat generated in the high-resistance start winding would cause disc 42 to deenergize the motor before the start winding could be damaged. The creep acting element 32 is designed to have a narrow differential (that difference in temperature which will cause contacts 40, 42 to open compared to that which will cause them to close), for example 1 or 2C, to insure that upon starting of the motor at any time the start winding is energized. Disc 72 has a much larger differential, in the order of 40C or more and is so chosen that its differential encompasses the differential of the creep element so that the start winding is in the circuit at the time the disc 72 snaps to a contacts closed position and so that the motor does not run on the start winding. It will be noted in FIGS. 2 and 8 that a projection 82 is formed in a cover 18 to limit overtravel of the free end of disc 72 in the contacts opening direction thereby avoiding undue stress of the disc as well as tending to cool any arcs occurring on opening of the disc. Placement of the heater underneath the blade prevents overheatingof the narrow differential bladewith concomitant deleterious effects in motors having appreciable current passing through the main winding since the blade moves away from the heater as it creeps open. The snap acting disc of course is not subject to the same problem since it deenergizes the device upon opening thereof.

It will be appreciated that the operation of the thermal elements 32 and 72 are interrelated and that it is important that they cooperate with one another: to start the motor as well as to protect it without having nuisance tripping and the like. This is accomplished in the present invention, primarily by using the single heater 52 which is in heat transfer relationship with both thermal elements. The creep acting blade is heated by a combination of internally generated heat due to PR heating from the start winding current in addition to heat generated by heater 52 from current passing through both windings. Hence a fast response is obtained for creep acting blade 32 even with motors having relatively low start winding current levels, in addition to employing the main winding current passing through the same heater 52 to insure that blade 32 is maintained in the open condition. Thus the device can be made to have a faster, more accurate response than prior art devices since both elements are calibrated to be effected by the same primary heat source.

In some applications it may be desirable to employ a snap acting disc rather than creep acting blade 32 when a somewhat shorter lived device is acceptable. As in the case of the creep acting blade, such a disc would be chosen so that it has a very narrow differential.

Another embodiment is shown in FIGS. 9 and 10. For certain applications it may be desirable to provide additional heat to the creep element 32 to cause element 32 not only to be more responsive on opening but also provide more heat to element 32 when the start winding is deenergized to insure that contacts 40, 42 will not reclose during normal run operation. For example in a situation where a motor having very low current levels is subjected to widely varying loads such as in the compressor of a refrigerator when the motor must run under both heavy and light loads. The following embodiment provides increased heat to maintain the creep acting blade in the open condition, even on very light load levels. This may be accomplished by employing a shunt heater 84 and is connected, as by welding, to body 46 of terminal 38 on one end and to terminal 44 at the other end thereof. The electrical resistance of heater 84 is chosen so that the current passing therethrough while sufficient to provide heat for element 32, is insufficient to cause overheating of the start winding. The combined heater is also modified in the embodiment. As shown in FIG. 9, heater 52' is located above both thermal elements to allow room for the shunt heater 84. Heater S2 is attached to welding slug 34 of terminal 38 on one end and, as in the previous embodiment, to welding slug 58 of the disc 72 mount. The shape of heater 52' in this embodiment is generally U-shaped with the bight portion extending between the two thermal elements. Raised portions 22 are extended beyond the component parts to provide protection for them as in the previous embodiment. it will be appreciated that the FIG. 9 heater 52 can be employed with or without the shunt heater 84, if so desired. For instance when used with miniaturemotors having very small current levels placement of the heater above the blade will make it more sensitive to the heat generated particularly as the blade creeps to the open position and therefore will hold the blade open at lower current levels.

As many changes could be made in the above constructions without departure from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense, and it is also intended that the appended claims shall cover all such equivalent variations as come within the true spirit and scope of the invention.

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

I claim:

1. Combined motor protector and relay apparatus comprising:

a base;

a first stationary contact'mounted on said base, a first thermal element comprising a snap acting disc mounted on the base and adapted to move into nd out of engagement with the first stationary contact;

a second stationary contact mounted on the base, a second thermal element comprising a creep acting blade mounted on the base and adapted to move into and out of engagement with the second stationary contact;

heating means located in the base in heat transfer relation with both the first and second thermal elements; and

means to provide electrical connection for the thermal elements, stationary contacts and heater with the second thermal element adapted to deenergize the start winding of a motor and the first thermal element adapted to deenergize the apparatus.

2. Apparatus according to claim 1 in which the heating means comprises a single heating element.

3. Apparatus according to claim 1 in which the snap acting disc moves toward the heating means when moving out of engagement with the first stationary contact and the creep acting blade moves away from the heating means when moving out of engagement with the second stationary contact.

4. Apparatus according to claim 1 in which both the snap acting disc and the creep acting blade move toward the heater when moving out of engagement with respective first and second stationary contacts.

5. Apparatus according to claim 2 in which the means to provide electrical connection includes electrically connecting the heater element serially between the first thermal element and the second then'nal element.

6. Apparatus according to claim 2 including a shunt heater electrically connected from the second stationary contact across the second thermal element.

7. Apparatus for starting and protecting electrical equipment having a main winding and an auxiliary winding comprising:

a base formed of electrically insulative material with a switch cavity defined therein and having at least three apertures extending from without the base into the switch cavity;

a first terminal received in one of the apertures, a

first stationary contact provided on the first terminal located within the switch cavity, a snap acting disc cantilever mounted on the base within the switch cavity and having a free distal vend, a first movable contact mounted on the free distalend of the disc and adapted to move into and out of engagement with the first stationary contact;

a second terminal received in another one of the apertures, a second stationary contact provided on the second terminal located within the switch cavity, a third terminal received in another one of the apertures and having a portion located within the switch cavity, a creep acting blade cantilever mounted on the portion of the third terminal and having a free distal end, a second movable contact mounted on the free distal end of the blade and adapted to move into and out of engagement with the second stationary contact;

an electrical resistance heater having two ends, one end electrically connected to the disc and the other end electrically connected to the third terminal, the heater being positioned so that it is in heat transfer relation with both the disc and the blade; and

a cover enclosing the switch cavity, the first terminal connectable to a power source, the second terminal connectable to the auxiliary winding and the third terminal connectable to the main winding.

8. Apparatus according to claim in which the snap acting element and the creep acting blade are positioned side by side and lie in respective parallel planes.

9. Apparatus according to claim 9 in which a first portion of the heater is positioned intermediate the cover and the snap disc and a second portion of the heater is positioned intermediate the base and the blade.

10. Apparatus according to claim 8 in which a raised platform is provided in the base on which the creep acting blade is mounted, a groove is defined in the platform running in a direction transversely to the blade and communicates with one of the apertures in the base, the third terminal forms a first leg and extends through the aperture in communication with the groove and depends from a body portion received in the groove, a second leg extends from the body portion parallel to the platform surface on which leg the blade is cantilever mounted, and a third leg extends from the body portion parallel to the platform surface but in an opposite direction to that of the second leg, an end of the heater element being attached to the third leg.

1 1. Apparatus according to claim 8 in which the base is generally rectangular in plan view and includes upstanding projections extending from the base on at least two diametrically opposite corners to provide protection for the parts mounted in the switch cavity.

12. Apparatus according to claim 8 in which a fourth aperture is defined in the base, an eyelet is received in the aperture, and a splined stud mounting the disc is telescopically received in the eyelet.

13. Apparatus according to claim 8 in which a first portion of the heater is located intermediate the creep acting blade and the cover and a second portion of the heater is located intermediate the snap acting blade and the cover.

14. Apparatus according to claim 14 in which a shunt heater is connected between the first terminal and the third terminal and is intermediate the blade and the base.

15. Apparatus according to claim 8 in which a projection extends downwardly from the cover and terminates at a position to limit the opening movement of the free distal end of the snap acting blade,

16. Apparatus according to claim 8 In which the creep acting blade is generally trapezoidal in shape extending from a rectangular mounting tab and the snap acting blade is generally rectangular in shape and is a fully formed disc. 

1. Combined motor protector and relay apparatus comprising: a base; a first stationary contact mounted on said base, a first thermal element comprising a snap acting disc mounted on the base and adapted to move into nd out of engagement with the first stationary contact; a second stationary contact mounted on the base, a second thermal element comprising a creep acting blade mounted on the base and adapted to move into and out of engagement with the second stationary contact; heating means located in the base in heat transfer relation with both the first and second thermal elements; and means to provide electrical connection for the thermal elements, stationary contacts and heater with the second thermal element adapted to deenergize the start winding of a motor and the first thermal element adapted to deenergize the apparatus.
 2. Apparatus according to claim 1 in which the heating means comprises a single heating element.
 3. Apparatus according to claim 1 in which the snap acting disc moves toward the heating means when moving out of engagement with the first stationary contact and the creep acting blade moves away from the heating means when moving out of engagement with the second stationary contact.
 4. Apparatus according to claim 1 in which both the snap acting disc and the creep acting blade move toward the heater when moving Out of engagement with respective first and second stationary contacts.
 5. Apparatus according to claim 2 in which the means to provide electrical connection includes electrically connecting the heater element serially between the first thermal element and the second thermal element.
 6. Apparatus according to claim 2 including a shunt heater electrically connected from the second stationary contact across the second thermal element.
 7. Apparatus for starting and protecting electrical equipment having a main winding and an auxiliary winding comprising: a base formed of electrically insulative material with a switch cavity defined therein and having at least three apertures extending from without the base into the switch cavity; a first terminal received in one of the apertures, a first stationary contact provided on the first terminal located within the switch cavity, a snap acting disc cantilever mounted on the base within the switch cavity and having a free distal end, a first movable contact mounted on the free distal end of the disc and adapted to move into and out of engagement with the first stationary contact; a second terminal received in another one of the apertures, a second stationary contact provided on the second terminal located within the switch cavity, a third terminal received in another one of the apertures and having a portion located within the switch cavity, a creep acting blade cantilever mounted on the portion of the third terminal and having a free distal end, a second movable contact mounted on the free distal end of the blade and adapted to move into and out of engagement with the second stationary contact; an electrical resistance heater having two ends, one end electrically connected to the disc and the other end electrically connected to the third terminal, the heater being positioned so that it is in heat transfer relation with both the disc and the blade; and a cover enclosing the switch cavity, the first terminal connectable to a power source, the second terminal connectable to the auxiliary winding and the third terminal connectable to the main winding.
 8. Apparatus according to claim in which the snap acting element and the creep acting blade are positioned side by side and lie in respective parallel planes.
 9. Apparatus according to claim 9 in which a first portion of the heater is positioned intermediate the cover and the snap disc and a second portion of the heater is positioned intermediate the base and the blade.
 10. Apparatus according to claim 8 in which a raised platform is provided in the base on which the creep acting blade is mounted, a groove is defined in the platform running in a direction transversely to the blade and communicates with one of the apertures in the base, the third terminal forms a first leg and extends through the aperture in communication with the groove and depends from a body portion received in the groove, a second leg extends from the body portion parallel to the platform surface on which leg the blade is cantilever mounted, and a third leg extends from the body portion parallel to the platform surface but in an opposite direction to that of the second leg, an end of the heater element being attached to the third leg.
 11. Apparatus according to claim 8 in which the base is generally rectangular in plan view and includes upstanding projections extending from the base on at least two diametrically opposite corners to provide protection for the parts mounted in the switch cavity.
 12. Apparatus according to claim 8 in which a fourth aperture is defined in the base, an eyelet is received in the aperture, and a splined stud mounting the disc is telescopically received in the eyelet.
 13. Apparatus according to claim 8 in which a first portion of the heater is located intermediate the creep acting blade and the cover and a second portion of the heater is located intermediate the snap acting blade and the cover.
 14. Apparatus according to claim 14 in which a shunt heateR is connected between the first terminal and the third terminal and is intermediate the blade and the base.
 15. Apparatus according to claim 8 in which a projection extends downwardly from the cover and terminates at a position to limit the opening movement of the free distal end of the snap acting blade.
 16. Apparatus according to claim 8 in which the creep acting blade is generally trapezoidal in shape extending from a rectangular mounting tab and the snap acting blade is generally rectangular in shape and is a fully formed disc. 